We investigated the optical properties of both arterial thormbi (AT) and the surrounding vessel wall (VM). Canine carotid arteries in 9 animals were traumatized with a forceps to promote platelet adhesion during a subsequent 60 minute perfusion period. Thrombin and whole blood were injected and the artery was ligated at both ends of the segment, creating a mixed platelet and fibrin thrombus. Using an integrating sphere spectrophotometer, transmission (T) and reflectance (R) were measured and the absorption (A) for ~25 nm AT samples (n=21) and for ~220 nm VW amples (n=9) were studied versus wave length (WL). The ratio of A for AT versus VW is 7:1 for light of a WL of 480-510 nm (p<0.001). Higher ratios are obtained at shorter (390-480 nm) and longer (510-580 nm) WL. Above 600 nm there is similar A by both tissues. We conclude that 480-510 nm laser irradiation provides a 7-Fold selectivity for AT versus VW and deeper penetration of light into the AT than do WL below 390 nm and above 580 nm, which may increase the volume of ablation and yield a more efficient, selective process.
Waltenberger J, Jacques S, Gregory KW, Optical properties of arterial thrombi and arterial wall in the visible spectrum: basis for pulsed dye laser thrombolysis. European Congress of Cardiology, 1990.